1. Field of the Invention
The present invention relates to a lighting unit using two types of light sources, to a backlight unit including such a lighting unit, and to a liquid crystal display device equipped the backlight unit.
2. Description of the Related Art
A liquid crystal display device is usually configured such that a backlight unit supplies a display light since a display element is non-emissive. As FIG. 6 illustrates, there is a configuration where an optical member such as a diffusing plate (not shown in FIG. 6) is combined with a lighting unit 100 that includes a plurality of aligned white light sources 101 such that the display light is provided uniformly in an in-plane direction of a display plane of the display device.
Fluorescent lights are usually used as white light sources 101 in the lighting unit 100. The use of fluorescent lights is associated with such a problem that color purity of display light generated by the fluorescent lights is low since light purity of R is generally lower than that of G or B in the fluorescent lights.
Therefore, as an art improving color reproducibility of an image on the liquid crystal display device, Japanese Unexamined Patent Application Publication No. 2004-139876 discloses a backlight unit as illustrated in FIG. 7, which includes optical members (not illustrated in FIG. 7) and a lighting unit 110 including two types of light sources; fluorescent lights 111 and LEDs (Light Emitting Diode) 112.
In the lighting unit 110, red spectrum characteristics are eliminated from the fluorescent lights 111; therefore, the fluorescent lights 111 having only blue spectrum characteristics and green spectrum characteristics are used. Combinational use of the fluorescent lights 111 with the LEDs 112 having red spectrum characteristics generate high color purity in R, G, and B. As a result, the lighting unit 110 provides high color reproducibility.
Japanese Unexamined Patent Application Publication No. 2003-187623, meanwhile, discloses a lighting unit including LEDs of plural types for emitting light of different colors.
However, the conventional configuration disclosed in Japanese Unexamined Patent Application Publication No. 2004-139876 has the following problem.
That is, in the lighting unit 110 in Japanese Unexamined Patent Application Publication No. 2004-139876, the two types of light sources must be arranged in an irradiation plane without overlapping each other. Therefore, the lighting unit 110 cannot obtain the uniform display light in both types of light sources simultaneously.
Take FIG. 7 as an example: when a pitch between neighboring fluorescent lights 111 is 2L, a pitch between the endmost fluorescent light 111 and an end portion of the lighting unit 110 is L; therefore, light outgoing from the fluorescent lights 111 will be uniform. On the other hand, the LEDs 112 are aligned respectively between the neighboring fluorescent lights 111; therefore, when a pitch between the neighboring LEDs 112 is 2L, a pitch between the endmost LED 112 and the end portion of the lighting unit 110 is 2L. As a result, the light intensity of the light outgoing from the LEDs 112 is insufficient at the end portions. Thus, the display light around the end portions of the lighting unit is bluish due to insufficient red light intensity.